Conventionally, for example, JP 2014-77645 A proposes a vibration sensing device in which an offset is adjusted. In JP 2014-77645 A, a DC component of the measured vibration data is adjusted to zero by, for example, an adjustable trimmer or digital processing (offset adjustment) to set a trigger level to a proper value. JP 2009-168509 A proposes a vibration warning device in which a user can set a threshold of warning display after startup. In a power device controlling method proposed by JP 2013-088314 A, an average value of vibration acceleration data measured with an acceleration sensor is calculated within a predetermined time, a reference value that is of basic vibration data in a steady state is always calculated by a moving-average method by repeatedly calculating the average value, an earthquake generation determination part compares the reference value calculated with a reference value calculator to the real-time acceleration data measured with the acceleration sensor, and the earthquake is determined when a difference between the real-time acceleration data and the reference value exceeds a predetermined threshold. JP 2013-108847 A proposes a seismometer that monitors whether a noise level exceeds a given threshold, and an abnormal annunciation signal is transmitted to a central control device constituting a seismometer abnormality monitoring system on the assumption that a delay of earthquake detection is generated when the noise level exceeds the threshold. In a technology proposed by JP 2013-108848 A, an initial value of the noise level is repeatedly calculated until becoming a proper value, which is previously fixed as no delay of the earthquake detection.
The seismic sensor in which a microcontroller is used can obtain an index value for evaluating a size of the earthquake through calculation processing, while the power consumption of the seismic sensor tends to increase compared with a conventional mechanical seismic sensor in which a current is passed by the vibration. It is desirable to particularly reduce standby power for a battery-driven device provided in a meter box like the seismic sensor that is used to cut off gas or electricity during the generation of the earthquake. However, depending on an environment where the device is used, the noise is also measured due to passage of a vehicle or construction, and the noises are measured at various levels. The power consumption of the seismic sensor increases when the false detection of the environmental noise is repeatedly generated. The false detection cannot completely be removed only by what is called the offset adjustment.